Electrical insulation

ABSTRACT

Thin electrical insulation having a first layer of resin impregnated micaceous paper, superimposed thereon a second layer of spaced flattened glass yarns and superimposed thereon a third layer of polymer film is particularly adapted to the insulation of relatively small conductors and for use at elevated temperatures.

United States Patent 161/206,231; 174/120 C, 120 SR, 121 R, 121 SR, 122R, 122 G, 122 C, 124 R, 124 G, 124 GC POLYMER FILM FLATTENED Herman 1 1Feb. 18, 1975 1 ELECTRICAL INSULATION [56] References Cited [75]Inventor: Clairmont J. Herman, Schenectady, UNITED STATES PATENTS NY3,019,286 1/1962 Anderson 174/121 Assignee Gene a Electric p y,3,523,061 PUI'VIS Schenectady, N'Y 3,560,320 2/1971 Letteron 161/171 v 11 Filed! J 1 1972 Primary ExaminerGeorge F. Lesmes 21 APPL NO; 2 2 113Assistant Examiner-Charles E. Lipsey 52 11s. c1 161/143, 161/163,161/171, 1571 ABSTRACT 161/194, 16 174/120 Thin electrical insulationhaving-a first layer of resin 1 1 G impregnated micaceous paper,superimposed thereon It. a second layer of spaced flattened glass yamsand u- [58] Field 01 Search 161/143, 163, 171, 194, p rimposed thereon athird layer 0f polymer film is particularly adapted to the insulation ofrelatively small conductors and for use at-elevated temperatures.

4 Claims, 1 Drawing Figure ESlN-IMPREGNATED MlCA PAPER PATENTEB I 8i975'3867. 245

POLYMER FILM FLATTENED GLASS RESINIMPREGNATED MICA PAPER 1 ELECTRICALINSULATION This invention relates to composite insulating material. Moreparticularly, it relates to new and improved insulating material insheet or tape form and more spetos, mica flake and other inorganic flakematerial such as glass flakes, using glass or other inorganic fabric asa reinforcing medium, are well known. However, such insulationcontaining woven fabric such as of glass cannot be conveniently wound onsmall conductors of the order of 50 mils in diameter without excessivefraying particularly at elevated temperatures where any organic bondingmaterial would have been burned off. Asbestos acts in much the same wayas glass fabric in that it tends to fray and disintegrate unless bondedwith an inorganic heat-resistant material such as ceramic which thenrenders the conductors inflexible and the insulation friable andphysically delicate. The use of mica flakes in such tapes is alsolimiting in that relatively small conductors cannot be conformably woundwith the tape containing relatively large mica flakes. It has also beensought to use mica paper or reconstituted mica or similar material withglass fabric reinforced in-' sulation, and while the mica paper portionof the tape is conformable in and of itself, the tape is limited in suchcharacteristic by the presence of the glass fabric. From the above itwill be quite evident that there is a need for readily conformable andflexible electrical insulation which at the same time will retain itselectrical insulating and physical qualities at elevated temperatures atwhich any initial organic bonding material may have been essentiallyremoved by heat.

A principal object, therefore, of the present invention is to providesuch readily conformable and flexible electrical insulation which willretain suitable electrical insulating and physical characteristics atnormal and elevated temperatures.

Briefly stated, the present invention relates to electrical insulationin sheet or tape form which has a first or base layer ofresin-impregnated mica paper, a second superimposed layer of a pluralityof generally lengthwise disposed, flattened glass yarns, and optionallya third adherent layer of polymer or resin film. The material isparticularly characterized in that it can be wrapped conformably onrelatively small conductors or structures and will remain flexible andretain its electrical insulating qualities even at elevated temperaturesat which any organic resin binder or adhesive or impregnant would havebeen incinerated.

Those features of the invention which are believed to be novel are setforth with particularity in the claims appended hereto. The inventionwill, however, be better understood and further advantages and objectsthereof appreciated from a consideration of the following descriptionand the drawing in which the single FIGURE illustrates a preferredembodiment of the invention in tape form.

The mica paper or reconstituted mica which has been found to be usefulin connection with the invention can be prepared by any of a number ofprocesses including but not limited to those described in US. Pat. Nos.

2,549,880; 2,614,055; 2,709,158; 2,405,576 and 3,110,299. While the micapaper can be of any desired thickness commensurate with the particularapplication, it has been found that particularly in the wrapping ofsmall conductors of the order of 50 mils, such mica paper having athickness of about 1.5 to 2 mils is preferred.

The glass yarn which is useful in connection with the invention rangesgenerally from about 0.5 mil in diameter to about 3 mils and is made up,typically, of bundles of filaments which are twisted in well knownfashion to form the yarn. In actual use, the glass yarn is normallypartially flattened as will be described hereinafter. Where an overlyingfilm is indicated, any of a number of resinous or polymer films can beused including the various polyesters, polysulfones, polyethylene,polypropylene, polybutylene, polystyrene, polyvinyl acetal,polyacrylate, cellulose acetate, cellulose acetobutyrate, polyvinylacetal, polycarbonate, and the like, such film materials being wellknown to those skilled in the art.

Any of a number of polymeric materials, also well known to those skilledin the art, can be used to impregnate the mica paper layer and to adhereany overlying film to the substrate. However, it is preferred to use insuch roles organic polysiloxanes which are in and of themselvesrelatively high temperature resistant materials. Typical of thosematerials useful as an adhesive is General Electric organopolysiloxaneSR-5l6 which is essentially a mixture of silanol stoppeddimethylpolysiloxane having a viscosity of from about 1 million to 40million cps at 45C and MO resin where M is (C a )s 112 Q is $10 and theratio of M/Q is .55-.65/1 A typically useful mica paper impregnatingmaterial is General Electric SR-23l which is a 60 percent solution inxylene of a mixture of silanol stopped dimethylpolysiloxane fluid havinga viscosity of to 1000 cps at 25C MQ resin as above, and additional MQresin where the ratio of M/Q is .9-l/l, along with a small amount ofcatalyst such as cerium compound.

The following example illustrates the practice of the invention, itbeing realized that it is not to be taken as limiting in any way.

Mica paper having a thickness of about 1.7 mils was impregnated with theabove SR-23l resin with a kiss coater and oven cured at a rate of about10 ft/minute at C, the oven dwell time being about 5 minutes to give afinal resin content ranging from about 1.5 to 4 percent by weight of themica paper. It has been found that less than about 1.5 percent by weightof resin detracts from the water repellant characteristic of the micapaper which tends to disintegrate when exposed to moisture. On the otherhand, over about 4 percent by weight of resin content tends to causeblocking of the mica paper when it is wound up. The impregnated micapaper is next kiss coated with the above described SR-5l6 adhesive as a15 percent solution in toluene and treated in an oven at a temperatureof from about 40C to 100C and preferably at about 70C to remove most ofthe solvent and provide a tacky surface. Next, glass yarn having about200 filaments each about 0.00035 inch in diameter is fed on to the tackymica paper surface, the yarns being spaced to give about 18 to 20 yarnsper inch, the composite material being immediately fed through niprollers to flatten the glass yarns to the desired degree usually aboutone half the thickness. Generally speaking, while unflattened glassyarns can be used in certain applications, they tend to make thefinished product relatively thick. At the same time, the flatteningdisperses the glass filaments and provides more protection andreinforcement to the mica paper and with extreme flattening causes theglass filaments to cover essentially the entire surface of the micapaper and provides a high degree of resistance against puncture. Theoptional surface film of mil Mylar polyethylene terephthalate polyestermay be first lightly treated with the above adhesive and thensuperimposed on the substrate using a nip roller or other convenientpressing means to provide the finished product shown in the drawing.Here a length of tape 1 with its first or base layer of micaceous paper2 and reinforcing lengthwise disposed flattened glass yarns 3 is shownwith the overlying resin film 4 partially removed. The mica paper orpaper of similar material provides an electrical insulating barrierwhich is supported and reinforced conformably by the glass yarns. Theoverlying film of resinous material aids in conformably wrapping ortaping the material particularlyv on small wires or conductors, thisfilm as well as resin adhesives and impregnants being essentially orwholly removed if the insulated conductor is exposed to incineratingtemperatures. The finished insulation in the form of tape an be used toconformably wind or insulate relatively small wires of the order of 50mils in diameter which can then be wound into strands or cables. Whilethe insulation is suitable for use at ordinary temperatures with itsdielectric strength of 1000 volts/mil, short time, step by step, using Ainch electrodes, it is particularly suitable for use at elevatedtemperatures where the impregnating and adhesive material issubstantially or wholly burned off or incinerated. It has been foundthat when so incinerated, strands or cables of such insulated wiressubstantially retain their flexibility and insulating qualities and areresistant to abrasion and physical punishment. This is as distinguishedfrom prior art materials which, particularly at elevated temperatures,either lose their electrical insulating qualities or are inflexible orbecome severely deteriorated physically as well as electrically. Thepresent insulation is particularly useful for thermocouple wires and thelike.

What I claim as new and desire to be secured by Letters Patent of theUnited States is:

1. Electrical insulating tape having a layer of resin impregnatedmicaceous paper, superimposed thereon a plurality of flattened glassyarns disposed in spaced, generally lengthwise parallel fashion andsuperimposed thereon a layer of polymer film.

2. Electrical insulation as in claim 1 wherein said resin isorganopolysiloxane.

3. Electrical insulation as in claim 1 wherein said polymer film is ofpolyester.

4. Electrical insulation as in claim 1 wherein said resin impregnatedmicaceous paper and polymer film are covered with an adhesive.

UNI'II'II.) S'IA'IES PA'lllN'l OFFICE (IER'IIFICA'FE ()F CORRECTIONtATtNI' NO. 3,867,245

DAtLt) February 18, 1975 mvr m ts Clairmont J. Herman It is certrtredthat error appears in the above-identified patent and that send LettersPatent are hcrutry corrected as shown below Column 4, line 29 (Claim 4)delete "covered" and substitute therefor --cohered Signed and sealedthis 29th day of April 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents and TrademarksAttesting Officer UNI'II'II.) S'IA'IES PA'lllN'l OFFICE (IER'IIFICATE()F CORRECTION tATtNt NO. 3,867,245

DAILI) February 18, 1975 tNvtNlumg Clairmont J. Herman tt is cerhtiedthat error appears in the above-identified patent and that shut LettersPatent mchcmhy COHCCICU as shown below,

Column 4, line 29 (Claim 4) delete "covered" and substitute therefor--cohered Signed and sealed this 29th day of April 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents and TrademarksAttesting Officer

1. ELECTRICAL INSULATING TAPE HAVING A LAYER OF RESIN IMPREGNATEDMICACEOUS PAPER, SUPERIMPOSED THEREON A PLURALITY OF FLATTENED GLASSYARN DISPOSE IN SPACED, GENERALLY LENGTHWISE PARALLEL FASHION ADSUPERIMPOSED THEREON A LAYER OF POLYMER FILM.
 2. Electrical insulationas in claim 1 wherein said resin is organopolysiloxane.
 3. Electricalinsulation as in claim 1 wherein said polymer film is of polyester. 4.Electrical insulation as in claim 1 wherein said resin impregnatedmicaceous paper and polymer film are covered with an adhesive.